Method of producing aluminized paper



5 Claims. '(Cl. 117 -70) The present invention is directed to coating and more particularly to the production of an aluminized paper.

A principal object of the present invention is to provide a process for producing aluminized paper having a shiny aluminum surfacef Another object of the invention is to provide a process of the above type which gives a .final product which is inexpensive as well as being satisfactory.

Still another object of the invention is to provide a process of the above type which furnishes an aluminized product having a strongly adherent aluminum coating.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps With respect to each of the others, and the product possessing the features, -prope'rties and the relation of components which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims. 7

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

Workers in the coating art have long endeavored to find methods of providing inexpensive metallic finishes for paper. In the past such finishes have usually been provided by laminating aluminum or other metallic foil to a paper base. In some cases, vacuum metallizing has been accomplished on paper bases which have been treated with an organic lacquer to provide a shiny, smooth surface. However, such lacquers are much too expensive for large-scale use and have not met with any appreciable commercial success. Equally, other treatments of the paper base such as sizing have been tried from time to time but these have been found to be lacking in certain respects, such as inadequate adherence of aluminum, excessive outgasing during coating, diffuse reflection of the final coating, and numerous other defects.

We have ascertained that water glass (hydrated sodium silicate), if properly applied to paper, makes an excellent base for alurninizing. In practicing the present invention, we have discovered that the water glass coating is preferably applied in two relatively thin films. These films are preferably on the order of about one pound of water glass per thousand square feet of paper. Thus, with two coatings, a final film containing about two pounds of water glass per thousand square feet of paper is obtained. This is enough to provide a relatively smooth, shiny base for the aluminum. It is also preferred that at least the first water glass coating be applied under pressure so that this film is mechanically worked into the surface of the paper. It has also been found highly desirable to bake each film separately. This baking is preferably accomplished in an oven Where the I St Patent t 2,897,095 C6 Patented July temperature :is -,on :the ordervof 17-0':25 0 :F. .and above. The oven also :advantageouslyrincludes a zslqutce'ofinfra red heat although the pnmarybaKingseems to bear:- complished by conduction from the hot :air in the oven. This baking -is preferably continued for a .sufiiciently long time, at the temperature employed, to remove a substantial amount of the water of hydration from the sodium silicate coating. jIt is believed that this may also accomplish a certainamount of conversiqn off the water glass to a silicon oxide. e

Paper, which has been treated in accordance with the above described techniques can .-be,-wi-thout ffurtlier treatment, placed in avac-uum tankwhich iszthien pumped-1o a free airpressure on the orderof =1 imicron-or so. The paper 'isthen aluminized by being passed ;over;a.'-sour;ee

of aluminum -vapors such &8 those illustrated :-in U18.

Patents 2,665,223- 4-5+6789, isSu idIa-nuary 4, .1954. If the pressuredur-ing coating remains'below about 5 .microns and preferably below :about 3- microns Hg Jabs, it has been found that ashiny, adherentlaluminum :fi'lm is obtained.

In a preferred embodiment .of the invention, a shiny, heat-reflecting paper is .pr0d-uced in accordance with the following non-limiting example:

A roll of 40 pound coffee-bag krafL-paper isco'aited with water glass applied by means of a doctor blade. This doctorblade rubs the .coating into thesurfaee of .the kraft paper and is prefer-ably soiadjusted as to PIQYide a coatingof-aboutl :pojund ofwaterglass ;per thousand square feet of paper. In a preferred embodiment-attire invention the water glass is a commercial sodium .silicate known as K brand, containing approximately 1 1 percent Na O and 31.9 percent :SiG ;-(we'ight ratio of NagozsiO of 122.90,). rn ixturehad a-specific gnavity of about 47 -,B. andaviseosity of about 9.6 poise's. The K brand had a sol-id ,contentof about 42.9 per: cent, the remainder being water. This was dilu-tedsomewhat by adding three quarts of water to 4.5 gallons of i .through a 12-foot drying oven which is maintained at about 170-190 R, the paper passing at a speed of about feet per minute through the oven. The paper is then given another coating of water glass of about ,the same thickness as the first coating and again dried under substantially the same conditions. Without further treatment, the thus coated paper is placed in a vacuum coating chamber. The coating chamber is pumped to a low total pressure on the order of 1 or 2 microns and the paper is passed over the source of aluminum vapors, the coated side facing the source. This provides a shiny, strongly adherent, opaque aluminum film on the paper.

While we do not fully understand all of the reasons. why the present invention produces such a superior product, there are certain physical chemical relationships; Water glass (hydrated sodium silicate) is an extremely complex chem-- ical. It can assume many different forms with numerous: It is believed that the baking treatment provides a surface for the water glass;

which may explain the excellent results.

ratios of atoms being possible.

film which is substantially free of water of hydration.

part, so as to provide considerable free silica.

3 mously reduces the surface the interstices between the fibers of paper. This is believed to decrease, correspondingly, the amount of adsorbed air and water vapor which is given off by the paper as it is unrolled in the vacuum chamber. This water glass film is believed to also serve, at least partially, as a vapor barrier for trapping, within the paper, gases and vapors which might otherwise be released during the very short time that the paper is exposed to the hot aluminum vapors and the radiant heat from the source of aluminum vapors. The fact that the water glass film has been at least partially dehydrated may also impart to the film desiccant properties which permit it to absorb water vapor diffusing slowly through the film.

While the specific example given above demonstrates one preferred embodiment of the invention, it should not be considered as limiting. Numerous other commercially available sodium silicates may be employed having a wide range of permissible viscosities, specific gravities and solidscontents. Equally, the ratio of sodium oxide to silicon dioxide can be widely varied. The range of temperatures utilized for drying the sodium silicate film can be considerably wider than the specific range of temperatures mentioned in the specific example, and flame drying can be employed where care is taken not to burn the paper. Numerous other techniques well-known in the art of coating papers can be employed in connection with the preparation of the silicate coating.

Since certain changes may be made in the above process and product without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process of coating paper to provide a shiny aluminum surface thereon which comprises the steps of applying a film of water glass to the paper, baking the water glass film at a temperature on the order of 170- 200 F., applying a second film of water glass over the first film, baking the second water glass film at a temperature on the order of 170-200 F. and above, and

area of the paper by filling passing the thus coated and baked paper over a source of aluminum vapors in a chamber evacuated to a free air pressure of less than 5 microns Hg abs. to deposit a thin adherent shiny film of aluminum on said baked water glass coating.

2. The process of claim 1 wherein each of said coatings contains about 1 pound of sodium silicate (on a dry basis) per 1000 square feet of paper.

3. The process of claim 1 wherein at least the first water glass film is applied under pressure.

4. The process of claim 1 wherein the paper base comprises a calendered kraft paper.

5. The process of coating paper to provide a shiny aluminum surface thereon which comprises the steps of applying a film of water glass to the paper, baking the water glass film ;for a sufiiciently long time to remove a substantial amount of the water of hydration, at least from the surface thereof, applying a second film of water glass over the first film, baking the second water glass film at a temperature above F. for a sufficiently long time to decompose an appreciable portion of the sodium silicate molecules at the surface of the film, and passing the thus coated and baked paper over a source of aluminum vapors in a chamber evacuated to a free air pressure of less than 5 microns Hg abs. to deposit aluminum on the coated paper, the first depositing aluminum forming complex aluminates and silicates with the sodium silicate decomposition products on the surface of the baked film.

References Cited in the file of this patent UNITED STATES PATENTS 1,281,108 Vaughn Oct. 8, 1918 2,362,884 Clark Nov. 14, 1944 2,501,563 Colbert et al. Mar. 21, 1950 2,568,004 Heyman Sept. 13, 1951 2,622,041 Godley Dec. 16, 1952 2,647,069 Stericker July 28, 1953 FOREIGN PATENTS 554,156 Great Britain Dec. 16, 1941 

1. THE PROCESS OF COATING PAPER TO PROVIDE A SHINY ALUMNUM SURFACE THEREON WHICH COMPRISES THE STEPS OF APPLYING A FILM OF WATER GLASS TO THE PAPER, BAKING THE WATER GLASS FILM AT A TEMPERATURE ON THE ORDER OF 170*200*F., APPLYING A SECOND FILM OF WATER GLASS OVER THE FIRST FILM, BAKING THE SECOND WATER GLASS FILM AT A TEMPERATURE ON THE ORDER OF 170*-200*F. AND ABOVE, AND PASSING THE THUS COATED AND BAKED PAPER OVER A SOURCE OF ALUMINUM VAPORS IN A CHAMBER EVACUATED TO A FREE AIR PRESSURE OF LESS THAN 5 MICRONS HG ABS. TO DEPOSIT A THIN ADHERENT SHINY FILM OF ALUMINUM ON SAID BAKED WATER GLASS COATING. 